One split second of drunken violence almost cost Jason Cavanough everything.

On Tuesday, the Scarborough father wiped tears from his face as a Wollongong District Court jury acquitted him of killing his cousin in a one-blow assault outside a Woonona restaurant in January, 2012.

The relief was palpable as he hugged a long line of supporters outside the court and rushed to phone his mother with the good news.

During the five-day manslaughter trial, the court heard a momentary burst of aggression - just one single push - was all it took to fracture Allan Neilson's face and send his head plummeting to the pavement on that fateful night.

Five months later, the 60-year-old was dead.

It was a life-changing end to an otherwise uneventful day, initially spent by Mr Cavanough and Mr Neilson drinking and playing pokies at the Collegians club.

They later went to dinner at the Emerald Chinese Restaurant with Mr Neilson's wife and Mr Cavanough's family, where things soon began to unravel.

Several diners witnessed Mr Neilson being aggressive towards Mr Cavanough, urging him to "settle" the dispute outside before exiting the restaurant in a huff.

The trial heard Mr Cavanough joined Mr Neilson on the footpath outside, but not immediately, before the pair became involved in an argument.

Giving evidence on Monday, witness Suzanne Cochrane described how she saw Mr Cavanough walk away from Mr Neilson before quickly changing his mind, dropping the plastic bags he was carrying and return to strike Mr Neilson in the face.

Mr Cavanough's own version of events, as told to the first police officer on the scene, contradicted this account.

"He's been hammering me all night in front of my kids ... he took a swing at me. He missed and I pushed him," he told Senior Constable James Sala.

The force of the push caused him to fall to the ground and smash his head on the pavement.

Mr Neilson suffered fractures to the base of the skull, left eye socket and upper jaw as a result of the incident.

Dr Thomas Gibson, a specialist in impact injury, told the trial the injuries were most likely caused by a strong, single blow to the front of his face, but could not rule out the possibility they were the result of his head impacting with the pavement.

The decision, described by presiding Judge Paul Conlon as a possible "sympathy verdict", was handed down by the jury of eight men and four women after less than three hours' deliberation.